diff --git a/Dockerfile.m4 b/Dockerfile.m4
index 982617e..8827b2f 100644
--- a/Dockerfile.m4
+++ b/Dockerfile.m4
@@ -10,7 +10,8 @@ SHELL ["/bin/sh", "-euc"]
 
 # Enable source repositories
 RUN <<-EOF
-	sed -i '/^Types: deb$/s/$/ deb-src/' /etc/apt/sources.list.d/ubuntu.sources
+	sed -i '/^Types: deb$/s/$/ deb-src/' /etc/apt/sources.list.d/debian.sources
+	sed -i '/^Components: main$/s/$/ contrib non-free non-free-firmware/' /etc/apt/sources.list.d/debian.sources
 EOF
 
 # Install packages